Reverse DNS Not Working on some Email Recipients

We host our email for thecomputerguy.co on an internal server.
Everything has been working fine for several years, but recently we have started getting bouce backs from various other servers.
They all seem to have the following error:

I have checked all the blacklists and we don't seem to be listed on any.
I have done a reverse lookup from several sites and they all seem to be responding with the correct rDNS.
Does anyone have any suggestions?

It does look right. Are you sure the emails are being sent from that mail server and not somewhere else? Is there a NATting router or something else in the way? If you hit up api.ipify.org (eg, with wget or curl) what IP address does it report?

I assume the mail server that rejected you didn't happen to include more information, right? Like the hostname it resolved?

The only other thing I can think of is that your mail server is being used to send spam - or even just relay mail for another domain. Can you see what emails are being bounced and confirm they're from you?

This has been fixed...
I was able to get in touch with a few of the domains that could not receive our mail and they were all using a Barracuda device.
It turns out the Barracuda saw the .co and assumed it was coming from Columbia and blocked our mail. So we renamed our server with a .org address and reconfigured the RDNS with the same .org address and all is well now.